1. Field of the Invention
This invention relates generally to a direct drive servomotor and, more particularly, to a partial arc curvilinear direct drive servomotor (PACDDS) system, featuring a customized partial arc curvilinear magnetic way assembly and a low inertial guided sliding coil assembly that is directly driven to slide along the curved magnetic way by electric power.
PACDDS is a structurally simple and compact yet finely controlled by a set of advanced closed-loop power electronics that consists of an encoder and a servomotor drive. It features great power efficiency and high loading capacity to drive a payload to implement a high dynamic angular motion and precision angular positioning. PACDDS is a key component to implement low size, weight, and power consumption (SWaP) airborne gimbals with fast and precision performance for advanced imaging system stabilization, pointing, tracking, scanning, and seeking. It can also be used for many other customized motion-controlled devices such as robotic arms.
2. Description of Related Art
Airborne multi-axis gimbals for a high-end mapping camera are generally not available as COTS especially if low SWaP and optimized performance for flexible motion profiles are needed. PACDDS was invented as a key component to implement a structurally simple, low SWaP multi-functional high performance airborne roll, pitch, yaw 3-axis gimbals that precisely drive a massive 18 lb balanced payload. Such a payload includes a large format digital camera and a big telephoto lens for advance photogrammetric application.
A prior art angular motion driving device for a gimbal generally consists of a circular or linear motor coupled with a set of mechanical transmission devices, such as a set of worm gear drive. Gimbals that use mechanical transmission devices are generally associated with a low efficiency and poor responsiveness caused by additional motion inertia and friction of the transmission. They are also poor in accuracy caused by transmission-induced mechanical hysteresis and backlash. PACDDS directly converts the supplied electric power into a desired curvilinear motion of an ironless light weight coil based mover sliding along a customized arc length at an optimized radius of a U-channel magnetic way without using any mechanical transmission components. Hence it is structurally simplified and eliminates completely the mechanical hysteresis and backlash position errors in our Gimbal design to ensure highly accurate and repeatable angular positioning. By adopting a high efficient power-electronics based motor driver with a precision optical encoder for closed loop motion control, PACDDS is very power efficient, acoustically quiet, and powerful to drive a massive payload for angular motion and stabilization.
U.S. Pat. No. 5,684,344 issued Nov. 4, 1997 to Seiji Takei discloses a drive unit which supports object to be moved and a driving device in the form of a linear electromagnetic actuator which drives the curved guide unit. A moving magnetic type of linear direct current motor is employed for the electromagnetic actuator. However, the device is neither designed with a light weight ironless forcer nor U-channel magnetic way of the present invention. It also does not disclose an advanced digital servo type for very precision closed loop motion control. Along with its magnetic field leakage and heavier moving mass design, it is not as responsive, powerful, precise and efficient as those of the present invention, the PACDDS. The PACDDS ironless motor has several advantages over iron core motors such as lower moving coil mass, lower inductance, lower losses, higher stiffness and higher peak force capacity resulting in higher bandwidth, higher acceleration, better velocity control, and reduced position settling time.
U.S. Pat. No. 6,442,851 issued Sep. 3, 2002 to Stephen J. Botos et al. discloses a low profile tilt stage used for precision motor control such as positioning optical fibers for fiber to fiber bonding comprising a planar base 10, a cradle 17 defining a cylindrical surface having a cylindrical axis parallel to the base 10, a tilt table 11 mounted on the cradle by curvilinear bearings 28, 29 for rotation around the cylindrical axis of the cradle 17 and the table 11, the motor comprising an armature winding 15 nestled in the cradle 17, a rare earth permanent magnet track mounted on the underside of the table 11, an encoder reader 30 fixed relative to the base, and an encoder scale fixed to the tilt table 11. However, only a single layer of magnet track is used that is mosaicked by several curved surface thin magnets, whereas the present invention comprises a U-channel magnetic way with two parallel flat magnet tracks facing each other with a forcer or armature winding sliding between and along the curved U-channel of two flat plates, where a much more uniform and stronger magnetic field works.